VRT as a Biomarker of Cerebellar Dysfunction in Chronic Cannabis Use

Summary

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Description

The subjects have to realize movements towards a target, at a digitizing tablet, holding a digitizing pencil. Visual feedback is projected on a screen surface in front of the subject, which hides the sight of actual movements from the latter. In the experimental condition of rotation, the experiment...

The subjects have to realize movements towards a target, at a digitizing tablet, holding a digitizing pencil. Visual feedback is projected on a screen surface in front of the subject, which hides the sight of actual movements from the latter. In the experimental condition of rotation, the experimenter introduces a rotation of 45 grades between the movement realized by the subject and the visual feedback that is provided on the screen. Then, the subject is provided with a strategy in order to overcome this perturbation: that is, to make the movement aiming 45 grades to the opposite direction from the introduced rotation. This explicit strategy leads to immediate correction of the error, but as the time passes subjects tend to commit more and more errors due to implicit motor adaptation. This happens because the motor control system tends to correct the perceived perturbation between the anticipated and the actual location of the hand in an automatic and unconscious way. The conflict between the implicit and explicit strategies has the surprising consequence of a persistent and accumulative deterioration of performance that can only be resolved when the participants abandon the explicit strategy. Subjects with cerebellar damage show deficits in implicit motor learning and for this reason they do not show this progressive deterioration of performance. Given that chronic cannabis abuse can lead to cerebellar damage, the investigators hypothesize that subjects from the experimental group 1 (cannabis use) will have a significant smaller directional error on the rotation condition than controls. A second hypothesis is that this effect will be cannabis-specific, due to the high CB1R concentration on the cerebellum, so the alcohol dependence group is expected to perform similarly to control group

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